1. Field of the Invention
The present invention relates, generally, to a method for controlling accesses to resources of a communication network and, more particularly, to a method of expanding time-division multiplex oriented communication networks, particularly time-division multiplex oriented subscriber access networks, for the utilization of current traffic types or services.
2. Description of the Prior Art
In current communication networks designed according to the asynchronous transfer mode (ATM), particularly in subscriber line networks or subscriber access networks such as those designed as passive optical networks (PON) or as fiber coax networks (also referred to as access networks), the available data transmission rate, or the available resources of the communication network, are divided into network termination units. Such units are connected to either the communication network or the communication terminal equipment connected to the network termination units.
The access of the network termination units, or of the communication terminal equipment to the transmission medium used in common (for example, light waveguide or radio channel), is controlled by an algorithm. Such algorithm is typically realized with hardware given the high transmission rates and given a plurality of connected terminal equipmentxe2x80x94a network termination unit requesting a communication network resource being therewith granted the access authorization, or access to the transmission medium used in common. For example, the publication xe2x80x9cNOVEL ALGORITHM FOR TIME DIVISION MULTIPLE ACCESS IN BROADBAND ISDN PASSIVE NETWORKS,xe2x80x9d International Journal of Digital and Analog Communication Systems, Vol. 6, pages 55-62 (1993), M. Glade and H. Keller describes a method for controlling accesses of network termination units to, predetermied resources of a subscriber line network configured as a passive optical communication network.
According to the disclosed method, a timer or counter for each network termination unit, that is started in the framework connection setups derived from the network termination units, is arranged in a network control unit that is centrally arranged in the subscriber line network and connected to each network termination unit. A timer runs down, or the counter reaches a predetermined value, as soon as a new data packet or a specifically reserved memory area is filled with payload data in an affected network termination unit. Such is intermediately stored for data transmission in a buffer memory likewise arranged in the network termination unit. The dimensioning of the counters arranged in the network control unit, or the dimensioning of the time until the expiration of a timer, occurs dependent on the data transmission rates respectively defined, or reserved, during the connection setups. A signalling signal indicating the expiration of a timer represents a network termination unit-associated request for a transmission authorization, or an access to the transmission medium used in common that is sequentially stored in a memory (for example, FTO memory), realized in the network control unit and used in common by all network termination units connected to the network control unit. The stored access requests are read out therefrom and communicated to the connected network termination units, or communication terminal equipment as transmission authorization. As a result, the access to the transmission medium used in common is granted. In the described method, for example, two timers can expire at the same time; i.e., two isochronic access demands would have to be stored and controlled. Since, however, two accesses at the same time are not possible, one of the two access requests is delayed until the current access of the other access request has been terminated. This delay is referred to as a xe2x80x9ccell delay variation.xe2x80x9d Given expiration of a plurality of timers at the same time, the value of the xe2x80x9ccell delay variationxe2x80x9d is correspondingly incremented.
It has likewise already been proposed that the access authorizations to the transmission medium used in common requested by the network termination units be directly acquired and stored by a central control Unit Thus, the requested accesss to the transmission medium used in common would be uniformly distributed.
A plurality of traffic types, or service offerings defined by the ATM Porum, are also known from the communication technology according to the asynchronous transfer mode (ATM). According to such technology, high bit rate data transmissions with various demands of, for example, bandwidth and delays are supported or offered by the traffic type; see xe2x80x9cATM and ATM-Management: die Basis fxc3xcr das B-ISDN der Zukunft; LAN-Kopplung xc3xcber ATM WANxe2x80x9d, Rxc3xcidiger Selling, Berlin, Offenbbach: VDE-Verlag, 1997, pages 282-284. For example, voice, images and data can be transmitted over the same terminals via a type of cell multiplex method. The quality of service (QoS) of the individual traffic types and some traffic parameters are negotiated before the connection setup in the framework of the CAC (connection admission control) and are defined in what is referred to as a traffic agreement. The following traffic types, or service offerings, are defined by the ATM Forum:
constant bit rate (CBR),
variable bit rate (VBR),
unspecified bit rate (UBR),
available bit rate (AR).
The traffic types CBR and VBR are particularly suited for applications with high QoS demands such as, for example, multimedia service or video conference circuits with qualitatively high-grade image transmission. In CBR and VBR services, the bandwidth represents an important traffic parameter that is characterize by the specification of a peak cell rate and that must be offered during the entire duration of the connection.
In the traffic type VBR, the further traffic parameters of xe2x80x9cmaximum throughput ratexe2x80x9d and xe2x80x9cmaximum cell transmission ratexe2x80x9d (in cells per second) are also taken into consideration in the connection set up, in addition to the peak cell rate. The maximum throughput rate limits the transmission duration of an ATM cell to the peak cell rate.
The traffic type UBR is a service wherein, by contrast to CBR and VBR, no fixed bandwidth is reserved and a cell loss rate also is not defined. The network, thus, need not offer any resources for a UBR connection that is to be set up, or that is requested.
The traffic type ABR represents a mixture of reserved bandwidth such as in CBR and VBR, and non-reserved bandwidth as in UBR.
The present invention is therefore directed toward expanding time-division multiplex oriented communication networks, particularly time-division multiplex oriented subscriber access networks for the utilization of current traffic types or services; for example, for utilization of multimedia applications.
In the inventive method for controlling access to resources of a communication network, at least two criteria are selected from the transmission-oriented and switching-oriented properties of the resources of the communication network. Time-division multiplex oriented sub-resources with at least one criterion are allocated to network termination units arranged in the communication network. An important aspect of the inventive method is that a waiting list is provided for each selected criterion, and access requests of the network termination units to the sub-resources are allocated dependent on the selected criteria of the corresponding waiting list with the corresponding waiting list-individual criterion. By cyclically processing the waiting lists, the access to the corresponding sub-resources is granted according to the allocated access requests.
A critical advantage of the inventive method lies in that current, particularly broadband-oriented data services, such as time-critical multimedia services, can be realized in existing communication networks or communication networks to be installed and, in particular, in the subscriber access networks, also referred to as xe2x80x9caccess networks,xe2x80x9d arranged therein. Waiting lists can be cost-beneficially realized by definable memory areas in a memory arranged in the communication network. As such, corresponding memory areas can be defined for an arbitrary plurality of criteria, wherein access requests of network termination units to sub-resources of the communication network are storable therein. Dependent on the memory area-individual criteria, the access requests stored in the individual memory areas are read out and the access to the transmission medium used in common is correspondingly granted to the respective network termination units. Advantageously, data services based on different traffic types (i.e., making use of different transmission rates and processing priorities), can be cost-beneficially realized and offered by the inventive method with the assistance of a transmission medium used in common by a plurality of network termination units. Modern information services such as, for example, video-on-demand enjoy a rapid spread and a high user acceptance due to the advantageous realization of different broadband-oriented data services in subscriber access networks and due to the cost-optimum integration connected therewith.
According to an advantageous development, one criterion represents the priority of information to be communicated with the assistance of the resources; for example, time-critical voice or video services with high priority or data transmission services exhibiting a low priority. A waiting list to which the access requests to the sub-resources are allocated dependent on the priority of the information to be communicated is provided for each criterion. By reading out the access requests from the individual waiting lists, the access to the sub-resources is granted to the network termination units dependent on the allocated, priority-specific access requests. In a further embodiment, the waiting lists with the highest priority are processed first.
For example, the priority is determined with the assistance of the transmissionoriented and switching-oriented properties of the resources of services or services classes to be realized. Given realization of the communication network by a communication network according to the asynchronous transfer mode, the priority is advantageously determined by the properties of traffic types or service offerings defined according to the ATM Forum. As a result of this advantageous realization, information or data services with the following traffic types or service offerings already defined by the ATM Forum can be realized:
constant bit rate (CBR),
variable bit rate (VBR),
unspecified bit rate (UBR),
available bit rate (ABR).